A gas turbine engine typically includes a fan section, a compressor, at least one combustor, and a turbine. The desire for improved performance and fuel efficiency in aerospace industry has produced continuous improvement in the specific thrust and specific fuel consumption of gas turbine engines. Accordingly current aircraft engine design trends shift towards higher bypass ratio, low fan pressure ratio type of fan designs for improved fuel consumption. In high bypass ratio arrangements, the propulsion fan section creates most of the thrust provided by the engine. Lower fan pressure ratios may lead to increased propulsive efficiency, and enable thermodynamic cycle changes for improved fuel efficiency along with significant noise reduction. In addition, to improve fuel efficiency, a smaller engine core is preferred to cut down on the total weight of the gas turbine engine. Consequently, the compressors may run hotter than conventional gas turbine engines.
On the other hand, gas turbine engines also typically have various components, such as gears and bearing, which benefit from lubrication and cooling. An oil supply system provides oil, or other lubricating liquid, to the components to complete the lubrication and cooling. Afterward, the oil is typically cooled by air-oil coolers (AOCs) positioned in a gas flow path of the gas turbine engine. AOCs are used in the lubricating systems of some turbine engines to reduce the temperature of the oil to a degree suitable for recirculation through the system. If the gas flow path has a relatively slow air flow, for example, in the case of a smaller core and lower fan pressure ratios, the AOC typically needs to become larger and taller to achieve the desired amount of cooling. A larger and taller AOC not only adds undesirable weight to the small core engine, but also presents a problem of fitting the AOC without excessive drag or nacelle structural issues since the available packaging volume in a small core engine is much smaller than that in a conventional engine. For example, extending the AOC into a bypass flow stream of the engine's propulsion fan would reduce the overall thrust output of the engine, thus, may run counter to the purpose of the small core engine design.
To better answer the challenges raised by the gas turbine industry to produce reliable and high-performance gas turbines engines, in particular, engines with a smaller core, it is therefore desirable to provide an improved AOC which efficiently cools the oil without disrupting the current small core engine design or reducing the thrust output of the engine.